The present invention relates to a method of manufacturing a compound body with a layer by applying a low pressure to the body in a porous state while dipping the body into a slurry of components of the layer material, whereafter the compound body is heat treated, e.g., by sintering.
In order to increase the wear resistance of a body exposed to wear without losing toughness, the body is often coated with a wear resistant layer. Such is the case for inserts for machining where one or more layers are applied using CVD- or PVD-technique. Layers deposited in this way are usually single phase and a suitable thickness is some ten microns. A limitation with such layers is that it is difficult to combine fine grain size, thick layers and good adhesion.
Applying a layer onto porous bodies by dipping is a suitable production method. This, however, leads often to problems with bubbling and blistering and an incompletely covering layer. The bubbling and blistering is due to the pore system in the body and is accentuated by coarse and/or unevenly distributed pores. A particularly unfavorable pore system is found in materials containing fibers and/or needle and/or plate-like single crystals.
When isostatically pressing a porous body, the body is usually enclosed in a dense enclosure in order to prevent the pressure medium from penetrating into the pore system of the body. The enclosure is usually a glass or a material which forms a glass at the heating temperature, which is applied in powder form. In order to avoid penetration of the glass into the pores of the body and/or its reaction with the same during the isostatic pressing, one or several intermediate layers are applied which acts as barrier or protective layers. After completion of the isostatic pressing, the glass as well as the intermediate layers are removed. The intermediate layers are generally applied by dipping the body into a slurry of components included in the layer material. However, due to bubbling and blistering during the dipping there are often hollows in the intermediate layer. Swedish patent application SE 9004134-4 discloses an improved method of applying such layers by dipping the body in a slurry of powdered material included in the layer whereby a subpressure is obtained in the porous body by at least one suction cup.